BlackSea: Radionuclides

Abstract

Anthropogenic radionuclide pollution of the Black Sea originated primarily from the atmospheric nuclear weapon tests carried out during the late 1950s and early 1960s before the signing of the Test Ban Treaty in 1963, and after the Chernobyl nuclear power plant (NPP) accident in April 1986. Chernobyl atmospheric fallout deposited 1.7–2.4 PBq of 137 Cs into the Black Sea surface, which temporarily increased the 137 Cs inventory of the 0–50 m surface layer by a factor of 6–10 in comparison with its pre‐Chernobyl value. The contribution of Chernobyl‐origin 90 Sr (0.1–0.3 PBq) from atmospheric fallout was lower in comparison with that of 137 Cs. A subsequent 90 Sr input from the Danube and the Dnieper Rivers (about 0.16 PBq) was an important contribution to the budget of this radionuclide in the Black Sea, while the riverine 137 Cs input (0.02–0.03 PBq) was insignificant. The decrease of the 137 Cs inventory in the surface layer after Chernobyl accident has been mainly controlled by vertical mixing, loss through the Bosporus Strait, and radioactive decay. The loss through the Bosporus accounted for 2–2.5% of the 137 Cs inventory. In the case of 90 Sr, these processes have been compensated by river inputs from the Dnieper and Danube up to 1994–1995 and partially after 2000. The vertical mixing of 137 Cs and 90 Sr was mainly effective within the 0–200 m layer. Sediment inventories of 137 Cs in the Danube and Dnieper delta regions exceeded by one order of magnitude the values in the slope zone and two orders of magnitude those in the deep basin. Because of the self‐cleaning processes, the current levels of anthropogenic radionuclides are relatively low in all the components of the Black Sea environment, and therefore do not pose any radiological problem. Doses to marine biota from 137 Cs and 90 Sr are several orders of magnitude lower than those from natural 210 Po.